Add VFS2 plumbing for extended attributes.

PiperOrigin-RevId: 286281274

6 files changed, 209 insertions, 2 deletions

diff --git a/pkg/sentry/vfs/file_description.go b/pkg/sentry/vfs/file_description.go
index 6575afd16..c5a9adca3 100644
--- a/pkg/sentry/vfs/file_description.go
+++ b/pkg/sentry/vfs/file_description.go
@@ -22,6 +22,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/context"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
+	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
@@ -212,7 +213,21 @@ type FileDescriptionImpl interface {
 	// Ioctl implements the ioctl(2) syscall.
 	Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error)
 
-	// TODO: extended attributes; file locking
+	// Listxattr returns all extended attribute names for the file.
+	Listxattr(ctx context.Context) ([]string, error)
+
+	// Getxattr returns the value associated with the given extended attribute
+	// for the file.
+	Getxattr(ctx context.Context, name string) (string, error)
+
+	// Setxattr changes the value associated with the given extended attribute
+	// for the file.
+	Setxattr(ctx context.Context, opts SetxattrOptions) error
+
+	// Removexattr removes the given extended attribute from the file.
+	Removexattr(ctx context.Context, name string) error
+
+	// TODO: file locking
 }
 
 // Dirent holds the information contained in struct linux_dirent64.
@@ -329,6 +344,38 @@ func (fd *FileDescription) Ioctl(ctx context.Context, uio usermem.IO, args arch.
 	return fd.impl.Ioctl(ctx, uio, args)
 }
 
+// Listxattr returns all extended attribute names for the file represented by
+// fd.
+func (fd *FileDescription) Listxattr(ctx context.Context) ([]string, error) {
+	names, err := fd.impl.Listxattr(ctx)
+	if err == syserror.ENOTSUP {
+		// Linux doesn't actually return ENOTSUP in this case; instead,
+		// fs/xattr.c:vfs_listxattr() falls back to allowing the security
+		// subsystem to return security extended attributes, which by default
+		// don't exist.
+		return nil, nil
+	}
+	return names, err
+}
+
+// Getxattr returns the value associated with the given extended attribute for
+// the file represented by fd.
+func (fd *FileDescription) Getxattr(ctx context.Context, name string) (string, error) {
+	return fd.impl.Getxattr(ctx, name)
+}
+
+// Setxattr changes the value associated with the given extended attribute for
+// the file represented by fd.
+func (fd *FileDescription) Setxattr(ctx context.Context, opts SetxattrOptions) error {
+	return fd.impl.Setxattr(ctx, opts)
+}
+
+// Removexattr removes the given extended attribute from the file represented
+// by fd.
+func (fd *FileDescription) Removexattr(ctx context.Context, name string) error {
+	return fd.impl.Removexattr(ctx, name)
+}
+
 // SyncFS instructs the filesystem containing fd to execute the semantics of
 // syncfs(2).
 func (fd *FileDescription) SyncFS(ctx context.Context) error {
diff --git a/pkg/sentry/vfs/file_description_impl_util.go b/pkg/sentry/vfs/file_description_impl_util.go
index aae023254..3df49991c 100644
--- a/pkg/sentry/vfs/file_description_impl_util.go
+++ b/pkg/sentry/vfs/file_description_impl_util.go
@@ -127,6 +127,31 @@ func (FileDescriptionDefaultImpl) Ioctl(ctx context.Context, uio usermem.IO, arg
 	return 0, syserror.ENOTTY
 }
 
+// Listxattr implements FileDescriptionImpl.Listxattr analogously to
+// inode_operations::listxattr == NULL in Linux.
+func (FileDescriptionDefaultImpl) Listxattr(ctx context.Context) ([]string, error) {
+	// This isn't exactly accurate; see FileDescription.Listxattr.
+	return nil, syserror.ENOTSUP
+}
+
+// Getxattr implements FileDescriptionImpl.Getxattr analogously to
+// inode::i_opflags & IOP_XATTR == 0 in Linux.
+func (FileDescriptionDefaultImpl) Getxattr(ctx context.Context, name string) (string, error) {
+	return "", syserror.ENOTSUP
+}
+
+// Setxattr implements FileDescriptionImpl.Setxattr analogously to
+// inode::i_opflags & IOP_XATTR == 0 in Linux.
+func (FileDescriptionDefaultImpl) Setxattr(ctx context.Context, opts SetxattrOptions) error {
+	return syserror.ENOTSUP
+}
+
+// Removexattr implements FileDescriptionImpl.Removexattr analogously to
+// inode::i_opflags & IOP_XATTR == 0 in Linux.
+func (FileDescriptionDefaultImpl) Removexattr(ctx context.Context, name string) error {
+	return syserror.ENOTSUP
+}
+
 // DirectoryFileDescriptionDefaultImpl may be embedded by implementations of
 // FileDescriptionImpl that always represent directories to obtain
 // implementations of non-directory I/O methods that return EISDIR.
diff --git a/pkg/sentry/vfs/filesystem.go b/pkg/sentry/vfs/filesystem.go
index 8011eba3f..b766614e7 100644
--- a/pkg/sentry/vfs/filesystem.go
+++ b/pkg/sentry/vfs/filesystem.go
@@ -186,6 +186,20 @@ type FilesystemImpl interface {
 	// UnlinkAt removes the non-directory file at rp.
 	UnlinkAt(ctx context.Context, rp *ResolvingPath) error
 
+	// ListxattrAt returns all extended attribute names for the file at rp.
+	ListxattrAt(ctx context.Context, rp *ResolvingPath) ([]string, error)
+
+	// GetxattrAt returns the value associated with the given extended
+	// attribute for the file at rp.
+	GetxattrAt(ctx context.Context, rp *ResolvingPath, name string) (string, error)
+
+	// SetxattrAt changes the value associated with the given extended
+	// attribute for the file at rp.
+	SetxattrAt(ctx context.Context, rp *ResolvingPath, opts SetxattrOptions) error
+
+	// RemovexattrAt removes the given extended attribute from the file at rp.
+	RemovexattrAt(ctx context.Context, rp *ResolvingPath, name string) error
+
 	// PrependPath prepends a path from vd to vd.Mount().Root() to b.
 	//
 	// If vfsroot.Ok(), it is the contextual VFS root; if it is encountered
@@ -208,7 +222,7 @@ type FilesystemImpl interface {
 	// Preconditions: vd.Mount().Filesystem().Impl() == this FilesystemImpl.
 	PrependPath(ctx context.Context, vfsroot, vd VirtualDentry, b *fspath.Builder) error
 
-	// TODO: extended attributes; inotify_add_watch(); bind()
+	// TODO: inotify_add_watch(); bind()
 }
 
 // PrependPathAtVFSRootError is returned by implementations of
diff --git a/pkg/sentry/vfs/options.go b/pkg/sentry/vfs/options.go
index 3ecbc8fc1..97ee4a446 100644
--- a/pkg/sentry/vfs/options.go
+++ b/pkg/sentry/vfs/options.go
@@ -101,6 +101,20 @@ type SetStatOptions struct {
 	Stat linux.Statx
 }
 
+// SetxattrOptions contains options to VirtualFilesystem.SetxattrAt(),
+// FilesystemImpl.SetxattrAt(), FileDescription.Setxattr(), and
+// FileDescriptionImpl.Setxattr().
+type SetxattrOptions struct {
+	// Name is the name of the extended attribute being mutated.
+	Name string
+
+	// Value is the extended attribute's new value.
+	Value string
+
+	// Flags contains flags as specified for setxattr/lsetxattr/fsetxattr(2).
+	Flags uint32
+}
+
 // StatOptions contains options to VirtualFilesystem.StatAt(),
 // FilesystemImpl.StatAt(), FileDescription.Stat(), and
 // FileDescriptionImpl.Stat().
diff --git a/pkg/sentry/vfs/testutil.go b/pkg/sentry/vfs/testutil.go
index 7a1d9e383..d94117bce 100644
--- a/pkg/sentry/vfs/testutil.go
+++ b/pkg/sentry/vfs/testutil.go
@@ -117,6 +117,26 @@ func (fs *FDTestFilesystem) UnlinkAt(ctx context.Context, rp *ResolvingPath) err
 	return syserror.EPERM
 }
 
+// ListxattrAt implements FilesystemImpl.ListxattrAt.
+func (fs *FDTestFilesystem) ListxattrAt(ctx context.Context, rp *ResolvingPath) ([]string, error) {
+	return nil, syserror.EPERM
+}
+
+// GetxattrAt implements FilesystemImpl.GetxattrAt.
+func (fs *FDTestFilesystem) GetxattrAt(ctx context.Context, rp *ResolvingPath, name string) (string, error) {
+	return "", syserror.EPERM
+}
+
+// SetxattrAt implements FilesystemImpl.SetxattrAt.
+func (fs *FDTestFilesystem) SetxattrAt(ctx context.Context, rp *ResolvingPath, opts SetxattrOptions) error {
+	return syserror.EPERM
+}
+
+// RemovexattrAt implements FilesystemImpl.RemovexattrAt.
+func (fs *FDTestFilesystem) RemovexattrAt(ctx context.Context, rp *ResolvingPath, name string) error {
+	return syserror.EPERM
+}
+
 // PrependPath implements FilesystemImpl.PrependPath.
 func (fs *FDTestFilesystem) PrependPath(ctx context.Context, vfsroot, vd VirtualDentry, b *fspath.Builder) error {
 	b.PrependComponent(fmt.Sprintf("vfs.fdTestDentry:%p", vd.dentry.impl.(*fdTestDentry)))
diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 7262b0d0a..e60898d7c 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -440,6 +440,93 @@ func (vfs *VirtualFilesystem) UnlinkAt(ctx context.Context, creds *auth.Credenti
 	}
 }
 
+// ListxattrAt returns all extended attribute names for the file at the given
+// path.
+func (vfs *VirtualFilesystem) ListxattrAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation) ([]string, error) {
+	rp, err := vfs.getResolvingPath(creds, pop)
+	if err != nil {
+		return nil, err
+	}
+	for {
+		names, err := rp.mount.fs.impl.ListxattrAt(ctx, rp)
+		if err == nil {
+			vfs.putResolvingPath(rp)
+			return names, nil
+		}
+		if err == syserror.ENOTSUP {
+			// Linux doesn't actually return ENOTSUP in this case; instead,
+			// fs/xattr.c:vfs_listxattr() falls back to allowing the security
+			// subsystem to return security extended attributes, which by
+			// default don't exist.
+			vfs.putResolvingPath(rp)
+			return nil, nil
+		}
+		if !rp.handleError(err) {
+			vfs.putResolvingPath(rp)
+			return nil, err
+		}
+	}
+}
+
+// GetxattrAt returns the value associated with the given extended attribute
+// for the file at the given path.
+func (vfs *VirtualFilesystem) GetxattrAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, name string) (string, error) {
+	rp, err := vfs.getResolvingPath(creds, pop)
+	if err != nil {
+		return "", err
+	}
+	for {
+		val, err := rp.mount.fs.impl.GetxattrAt(ctx, rp, name)
+		if err == nil {
+			vfs.putResolvingPath(rp)
+			return val, nil
+		}
+		if !rp.handleError(err) {
+			vfs.putResolvingPath(rp)
+			return "", err
+		}
+	}
+}
+
+// SetxattrAt changes the value associated with the given extended attribute
+// for the file at the given path.
+func (vfs *VirtualFilesystem) SetxattrAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *SetxattrOptions) error {
+	rp, err := vfs.getResolvingPath(creds, pop)
+	if err != nil {
+		return err
+	}
+	for {
+		err := rp.mount.fs.impl.SetxattrAt(ctx, rp, *opts)
+		if err == nil {
+			vfs.putResolvingPath(rp)
+			return nil
+		}
+		if !rp.handleError(err) {
+			vfs.putResolvingPath(rp)
+			return err
+		}
+	}
+}
+
+// RemovexattrAt removes the given extended attribute from the file at rp.
+func (vfs *VirtualFilesystem) RemovexattrAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, name string) error {
+	rp, err := vfs.getResolvingPath(creds, pop)
+	if err != nil {
+		return err
+	}
+	for {
+		err := rp.mount.fs.impl.RemovexattrAt(ctx, rp, name)
+		if err == nil {
+			vfs.putResolvingPath(rp)
+			return nil
+		}
+		if !rp.handleError(err) {
+			vfs.putResolvingPath(rp)
+			return err
+		}
+	}
+}
+
 // SyncAllFilesystems has the semantics of Linux's sync(2).
 func (vfs *VirtualFilesystem) SyncAllFilesystems(ctx context.Context) error {
 	fss := make(map[*Filesystem]struct{})